System of distribution



Jan, 15, 1929. 1,699,153

A. H. MITTAG I SYSTEI OF DI STRIBUTION Fil p 1923 2 Sheets-Sheet 1 Inventor: Albert 9 H. Mitt'ag,

y ,MA His Attorney.

Jan. 15, 1929.

A. H. MITTAG SYSTEM OF DISTRIBUTION Infant or Z Albert H. Mittag,

His Attorney.

Patented at 15,1929.

UNITED STATES PATENT OFFICE.

ALBERT E. IITTAG, OF SCHENECTADY, NEW YORK, ASSIGNOB TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

SYSTEM or DISTRIBUTION.

My present invention relates to systems of electrical distribution, and more particularly to systems'for supplying current from a direct current distribution system for the operation of alternating current consumption apparatus. i

One of the objects of my invention is to provide a simple, reliable and efficient apparatus for converting direct current into alternating current, which will not require for its operation any devices having moving parts.

A further object of my invention is to provide an apparatus for the purpose mentioned, which will be especially adapted for use in .connection with high voltage direct current distribution systems. v

In carrying my invention into effect I provide a plurality of transformer windings and supply current from the direct current source to the primary windings through a plurality of electron discharge valves; In order that these valves should operate the best efiiciency they should be controlled in such a way that current will flow only when the potential difference between the terminals is comparatively small, and substantially the maximum current carried by the valves should be permitted to flow therethrough during the entire period during which the valve is rendered conducting.

In order to provide efficient operation, as

pointed out above, the current wave flowing through the valves must depart materially from the 'sine wave becoming substantially rectangular. This will result in production in the secondary windings of the transformer of waves having pronounced harmonics, which in some cases may be objectionable.

Still another object of my invention is to provide anapparatus whereby the obj cationable harmonics in the secondary current, particularly the fifth and seventh will be largely eliminated.

The novel features which I believe to be characteristic of my invention are set forth d with particularity in the appended claims, my invention itself, however, both as to its organization andmethod of operation, to-

; gether with further objects and advantages .-thereof, will best be understood by reference to the following description taken in conthose waves which are produced in the diifer-.

ent windings.

I have indicated in Fig. l a plurality of electron discharge valves 1 to 12, inclusive for supplying current from the direct current distribution mains 13, 14; to the primary windings 15 to 26, inclusive, of twogthreephase transformers 27 and 28. The primaries of each transformerare connected in double Y with interphase transformers 29 and 30 between the two neutrals for maintaining the proper balance between the currents supplied to the two primaries. The secondary windings 31 and 32 of the transformers 27 and 28 are connected in extended delta in such a way that the primary terminal voltages of one transformer may be displaced by 30 from the primary terminal voltages of the other and the secondary voltages may be in phase for reasons which will be more fully explained later. This combination gives the equivalent of twelve phases for the primaries and the use of this large number of phases in combination with other expedients pro- Videdgives a substantial sine wave form of current in the alternating current mains 33, 34 and 35 even though the current supplied to each primary winding departs materially from the sine wave form.

Valves 1 to 12 are indicated as'being of the three-electrode type having the usual cathode 39, anode 40 and discharge controlling grid 41. These may be of the high vacuum thermionic type or may operate by gas ionization.

In order to secure the desired efficiency in operation these valves should be made conucting during approximately one-third of each cycle. The positive potential applied to the grids to render the valves conducting should also be impressed in such a way that the current through each valve may quickly build up to its maximum value. In order that commutation may be effected without setting up surges in the system the valve should also be rendered non-conducting at the instant when the current has fallen to zero, or substantially to zero. To secure these results substantially rectangular potential waves should beapplied to the grids of ,the valves if the valves are of the thermionic type. If the valves are of the ionization type all that is necessary is to supply to the grids a positive potential of short duration to permit the current tov start. In order to secure the desired potential waves for controlling the valves a series-of high potential low power, three-electrode thermionic valves 42 to 53 inclusive may be employed. The anodes of these valves are connected to the positive side of the direct current supply by means of the lead 54 through individual resistances 55. Controlling potentials of the grids of valves 42 to 53 are obtained from the alternating current distribution mains through the conductors 56, 57 and 58 which are connected to e uidistant points in the rmg winding 59, and y suitable adglustment of these ta s potentials of the desired phase may .be obtamed. The grid circuits of valves 42 to53 ma be completed through a winding 61, the middle point 62 of which is connected to the cathodes of the valves through the grid biasing battery 63.

The anodes of valves 42 to 53 are connected throu h condensers 64 to the primaries of transformers 65, the secondaries of which are connected in the grid circuits of valves 1 to 12. When the valves 42'to 53 are non-conducting their anodes will be at substantially the same potential as the positive side of the direct current supply. The charging current of condenser 64 will then induce in the secondaries of transformers 65 a current which will make the grids 41 negativeand prevent the flow of current through valves 1 to 12. As soon as valves 42 to 53 have been rendered conducting their impedance is greatly reduced and the main drop in their plate circuit-s occurs through resistances 55. As a result their plate potentials will be greatly lowered, the condensers 64 will discharge, and the currents in transformers 65 will reverse cans-- inggrids 41 to become positive and perm1t current to flow through valves 1 to 12. Thepotentials applied to the grids of valves 42 to 53 should be so chosen that the time reuired to change the impedance of the valves om the maximum to a minimum value will be much less than the time during which it is desired that current shall flow in valves 1 to 12. By this expedient substantially rec-' tangular current waves may be set up in valves 42 to 53 and substantially rectangular potential waves applied to the grids of valves '1 to 12. By the proper choice of the poten tials applied to the grids of valves 42 to 53 the duration of the positive potential wave applied to the grids of valves 1 to 12 may be made equal to the time during which it is desired to have current flow in valves 1 to 12. By suitable adjustment of the taps 60 the instants when the potentials applied to the grids of valves 1 to '12 change from negative to positive, may be made to correspond to the instants when it is desired that the currents should begin to flow in valves 1 to 12.

Any convenient form of frequency determining element may be connected to the alternating current distribution system for fixing the frequency of the alternating currents produced. In the system illustrated a rotary converter 66 is connected to the alternating currenfldistribution system and the speed at which the converter is operated may deter mine the frequency of the alternating currents produced. This converter may be used to charge a storage battery 67 for supplying low voltage direct current for any desired purpose; as for example, for heating the cathode of valves 42 to 53. The operation of the system described may be initiated by starting the rotary converter 66 from the storage battery 67.

1n the system shown in Fig. 1, four of the valves will be carrying current at any given instant and a change in admission of current from one valve to a succeeding valve will take place every thirty time degrees. The periods during which the different valves will be carryingcurrent and the changes during a complete cycle will be as follows:

1 1 1 ,1 2 2 2 2 3 a s a 5 5 e e 6 e 4 4 4 4 5 5 9 7 7 7 7 s s s s 9 9 a 11 11' 11 12 12 12 12 10 1o 10 10 11 sponding fundamental secondary voltages will be in phase.

The phase relations between the fundamental voltages and the seventh harmonics thereof set up in the different primary windings is indicated in Fig. 2. The curves A in this figure represent the voltages produced in the primary windings of one of the transformers and the curves B represent the voltages produced in the primary windings of the other transformer. It will be noted that the fundamental voltages of curve B lag behind those of curve A by 30. At any instant, however, such as that indicated by the vertical line C, D, the seventh harmonic of each phase indicated in curve B lags 210 behind the corresponding harmonic of curve A. By the extended delta arrangement of the secondary windings of the transformer the phase of" the secondary voltage produced by the fundamental of curve B is advanced 15 while the phase of the secondary voltages produced by the fundamentals of curves A is retarded 15 so that the two secondary voltages coincide in phase.

By the same procedure the phase of the sec ings are short circui-ted and as long as the currents supplied to the two sets of primary windings are equal no current of the seventh harmonic is supplied to the mains 33, 34

l and 35.

rality of valves,

posite that of the fundamentals so that when the phases of the fundamentals of curves G and F are respectively advanced and retarded 15 the phases of the fifth harmonic voltages are retarded and advanced 15 and thefifth harmonic voltages. of curves G are made to lag 30 more behind those of curves F. As a result the secondary voltages of the fifth harmonic produced in the secondary of one transformer will be displaced 180 from the secondary voltages of the fifth harmonic in the other transformer and the two voltages will be short-circuited in the transformer windings in the same way asthe voltages of the seventh harmonic.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. The combination in a system of electrical distribution of a source of direct current, two sets of three-phase primary transformer windings connected to said source through a plurality of valves, a three-phase secondary transformer winding associated with each set of primary windings said secondary windings being connected to a threephas distribution circuit, and means for supplying to one set of currents which are displaced in phase from those supplied to the corresponding windings of theother set, the two secondary windings being so related to the primary windings that the currents supplied thereto by the two sets of primary windings will be in phase.

2. The combination in a system of electrical distribution of a source of direct current, two sets of three phase primary transformer windings connected to said source through a plua three phase secondary primary windings transformer winding associated with each set of primary windings said secondary windings arranged to control the current transmitted between said cathode and anode, a' transformer comprising one winding connected to one of said circuits in extended delta and another winding connected to another of said circuits through said cathode and anode, and grid potential control means arranged to cause current impulses of substantially rectangular wave form to be transmitted through said cathode and anode.

4. The combination of the plurality of circuits, a group of primary windings, means connected between said group and one of said circuits for causing current impulses of substantially rectangular wave form to be successively applied to said windings, and a group of secondary windings arranged to supply to another of said circuits current impulses from which the fifth and seventh harmonies have been eliminated.

5. The combination of direct and alternating current circuits, a group of primary windings, means comprising a plurality of electrical valves connected between said group and said'd irect current circuit for causing current impulses of substantially rectangular wave form to be sucessively supplied to said windings, and a group of secondary windings arranged tosupply to said alternating current circuit polyphase currents from which the fifth and seventh harmonics have been eliminated.

6. The combination of a plurality of circuits, a group of primary windings, electrical valve means connected between one of said circuits and said windings, means arranged to cause current of substantially rectangular Wave form to be supplied from said circuit through said valve means successively to said windings, and a group of secondary windings arranged to supply to another of said circuits current impulses of a wave form different from that of the current supplied to said primary windings.

7. The combination of a plurality of circuits, electrical valve means comprising a plurality of anodes anda plurality of grids each arranged to control the current of a different one of said anodes, a group of windings each connected to one of said circuits through a different one of said windings, grid potenanother of said circuits current impulses of tial control means. arran ed to cause current a wave form difierent from the current 1mof substantially rectangu ar wave form to be pulses supplied to said first mentioned group; 10 suppliedvfrom said circuit through said an- In wltness whereof, I have hereunto set odes to said windings, and a second group of my hand this 11th day of September, 1923. windings inductively related to said first 1 mentioned group and arrangedto supply to ALBERT H. MITTAG.

. p 7 DIS LAIME 1,699,153.-Alben H. Mittag, Schenectady, N. Y. SYSTEMorDIs'rRIBU'rIofi; Patent dated. January 15, 1929. Disclaimer filed July 23, 1931 by-the assignee;Ge'rteral 7 Electric Company. v Therefore, enters'this disclaimer to claims 1, 2, 4, 5, 6, and -7 ot'said patent which iareinthe following words:-' 4 b I 1. The'combination a system of electrical distribution of a 'sourceiof direct l current, two sets of three-phaseprimary transformer windingsconnected .to said'i r source through a'plurality of valves, a 'three-phasetsecondary transformer winding associated with each set of primary windings said secondary windings being'connected to a three-phasedistribution circuit and means ffor supplying to oil's-set ofprimary windings currents which are displaced in phase from; those supplied to the corresponding windings of the other set, the two secondary windings being so related to the prim v mary-windings that the currents suppliedthereto by the two sets of primarywindings willbeinphase. 2. The combination 'ina system of electrical distribution of "a source'of direct current, two: sets of three-phase primary {transformer windings connected to said source through a plurality of valves, a three-phase seccndary transformer winding. associated with each set of primarywindings said secondaryilwindings beingilconriected to a three-phase distribution-circuit and means for supplying to one set of piimary windings currents which are displacedinjphase by thirty electrical degrees "from those supplied to the corresponding windings'of the other set, thetwo secondary windings being so related tothe primary windings that the currents sup'pliedtheretoby the twosets of primary windingswill-' heimphasexi f "y,

4. The .combinationof the plurality of circuits, Ya *igroup'of primarry windings, means connected between said group and {one 10f, saidy'circuitsjfforcausingfcurrent impulses of substantially rectaiigular'waye form l-tto; be isuceessiyelyflpplied' to saidwindings, and'a group of' secondary windingsarranged to eupplyj to auother.of said circuits current impulses from whic'h fthe djse'veuth, harmonics have been eliminated. a p .5. The combination of directand alternating current circuits, agroup ,ofprnnaryf 'windin gs means comprising a plurality oflelectrical yalves connected between said group and said direct. current circuit'l for; causing current impulses of. substantially rectangular wave form to be i successiyely supplied to said windings, and'a group of, secondary windings arrangedtoisupply tov said 'alteriiating current circuit polyphase "currents from which the fifth and seventh'harmonics have been'eliminated.

6. Theco'mbination of a plurality of circuits, a group of. Wifidings,.electrical'va'lve means'connected betwe 11 one of saidtcirc uits and ald windings,- means i 'arrangedito-cause current of'fsubstantially' rectangular wave fomijth be supplied from said circuitthrough said valvqmeans successively to said-windings, and a group of secondary windings 'arranged*to .-supply to another of said circuits current impulses -Of a' wave formydiflerent'from-thatof the current suppliedvto said primary windings. 7. Th combination of' a plurality of circuits, electrical value means'. comprising I a plurality of anodes and a'pluralityiof-grids leach arranged to control: the current of .a different one of saidanodes a group. of windingsfleach connected'toone of. said cir- 'cuits through a different one ofsaid electrical: -rvalvegineans, grid potential control means arranged to cause current of substantially rectangular waveform to vb e. supplied from said circuit throughsaid anodefs to s'aid 'winding's, and a second grou lof windings inductively related toflsaid first mentionedtgroup and? arranged, to supp y'to anotherof said circuitscurrent impulses of a 'wave form difierent from, the current impulses su" plied-to said first men-tibnal'-group.- H

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